A bloke is driving around in his Porsche in the countryside. He stops outside a field full of sheep, walks up to the shepherd and says, "I've got an offer. I'll guess how many sheep you've got in this field, and if I guess right, I get to take a sheep with me. If I guess wrong, you get my car."
The shepherd thinks he's on to a sure thing and agrees. "137" says the driver. "Damn me, you're right," says the shepherd and dutifully hands over a sheep. The man walks away, stuffs the sheep in his car and is about to drive away when the shepherd knocks on his window.
"I've got a proposal for you." says the shepherd. "If I can guess what you do for a living, I get to take your car. If I'm wrong, you can have all my sheep." "Done," says the driver. "You're a consultant,." says the shepherd. "Bloody hell, how did you guess?"
"Easy. You come in here uninvited, you tell me what I already know and then you charge me for it."